Cveto Klofutar

Viscosity of aqueous solutions of poly(ethylene glycol)s at 298.15 K

Abstract The viscosities of aqueous solutions of some poly(ethylene glycol)s (PEG) with nominal molecular weights ranging from 300 to 35 000 g mol−1 were determined up to a concentration of 0.3 g cm−3 at 298.15 K. From these data the intrinsic viscosity and the viscosity average molecular weight of the solute were calculated. The viscosity coefficients B were evaluated and hence the partial molar Gibbs free energy of activation of viscous flow of solute at infinite dilution was calculated and interpreted in terms of the relative effects of solute on the ground and transition state solvent. The hydration numbers were determined and compared with available values in the literature.

A volumetric study of aqueous solutions of poly(ethylene glycol)s at 298.15 K

Abstract The densities of aqueous solutions of some poly(ethylene glycol)s with nominal molecular weights ranging from 300 to 35 000 g mol −1 have been determined up to a weight molality of 0.7960 at 298.15 K. From these data, the apparent specific volume of the solute and the partial specific volume of the solute and solvent were calculated. The specific excess volume of the solutions and the coefficients of the virial expansion of the excess property were evaluated and interpreted in terms of solute–solute and solute–solvent interactions. From the partial specific volume of the solute at infinite dilution and the value of the average degree of polymerization, the partial molar volume of the repeating unit was evaluated, as well as the excluded volume between the solvent molecules and repeating unit, and the excess excluded volume representing the end-group effects.

Apparent molar volumes and expansibilities of 1-octanol, 1-nonanol, and 1-decanol in dilute cyclohexane solutions

The densities of solutions of 1-octanol, 1-nonanol, and 1-decanol in cyclohexane up to concentrations of 1.56 mol kg−1 were measured at temperatures between 20 and 60°C. The apparent molar volumes and expansibilities were found to be linearly dependent on solute concentration. The excess molar volume and the excess thermal expansion coefficient of the solute were derived from the partial molar volume of the solute at infinite dilution and the solute densities. In addition, the limiting partial molar volume of the solute is discussed in terms of the scaled particle theory.

Partial molar volumes and viscosity B coefficients of tri-n-dodecyl-, tri-n-decyl-, tri-n-octyl- and tri-n-hexyl-amines in benzene solutions

Abstract The partial molar volumes and viscosity B coefficients of tri-n-dodecyl-, tri-n-decyl-, tri-n-octyl- and tri-n-hexyl- amines in benzene solutions at 25°C have been determined. The partial molar volumes are described by the equation V − = 40·89 + 16·82 (±0·19)n , where n represents the number of CH2 groups in the investigated compounds. The values of B coefficients obtained increase with increasing number of carbon atoms in the alkyl chains and, contrary to the case of aqueous solutions, do not show a linear relation with partial molar volumes.

The rheological properties of Slovenian wines

Abstract Forty samples of bottled wines from Slovenia were characterised by standard chemical analysis. The effect of temperature on their density and viscosity was studied in the temperature range from 20°C to 50°C. From the density data the expansibility coefficients at 25°C and their temperature dependence were calculated. The viscosity of wine decreases non-linearly with increasing temperature. The experimental data were fitted to some theoretical models in order to describe the temperature dependence of the viscosity of wine. A modified Andrade equation was found to best describe this dependence. The activation energy for viscous flow of wine, calculated by the Arrhenius relation, varied from 18.63 kJ mol −1 to 20.25 kJ mol −1 . Correlations between the activation energy for viscous flow and the concentrations of solutes other than ethanol were estimated. A significant correlation between the osmolality of wine and its viscosity was found for all wines investigated.

Partial molar volumes and partial molar expansibilities of cholesterol in some aprotic solvents

Abstract The densities of solutions of cholesterol (up to 0.4 mol kg −1 ) in benzene, toluene, carbon tetrachloride, chloroform or 1,2-dichloroethane were measured at 293, 298, 303, 313, 323 and 333 K. The partial molar volumes and partial molar expansibilities of the solute were found to be independent of concentration. The thermal expansion coefficients of the solute in the studied solvents tended to decrease slightly with increasing temperature. The thermal expansion coefficients of the investigated solutions decreased with increasing concentration. In addition, the partial molar volumes of the solute at infinite dilution are discussed on the basis of scaled particle theory. The “solvent effect” on the partial molar volume of the solute was found to be due mainly to cavity formation and intermolecular dispersion forces.

Conductivity of some tetra-n-alkylammonium salts of pectic acid

From commercially available pectin, (OBIPEKTIN AG), pectic acid was isolated by alkaline catalysed hydrolysis and physicochemically characterized. The conductivities of aqueous solutions of tetramethyl-, tetraethyl-, tetra-n-propyl- and tetra-n-butyl pectate were determined. The concentration dependence of the conductivity as well as the conductometric titration of the investigated systems exhibited typical polyelectrolyte behaviour. The mobility of the polyelectrolyte solute was found to be influenced by the nature of the counterion. The calculated values of the molar conductivity deduced on the basis of the Manning limiting law were found to be lower than the experimental ones. The fraction of free counterions was evaluated and found to depend on the concentration and on the nature of the counterion.

Structures of artificial sweeteners--cyclamic acid and sodium cyclamate with other cyclamates.

In the course of a study on artificial sweeteners, new crystal structures of cyclamic acid, sodium cyclamate, potassium cyclamate, ammonium cyclamate, rubidium cyclamate and tetra-n-propylammonium cyclamate have been determined. Cyclamic acid exists in its zwitterionic form in the crystalline state. The zwitterions are connected through hydrogen bonds of the N-H...O type to form two-dimensional sheets. The sodium, potassium, ammonium and rubidium cyclamates are isostructural, with the cyclamate moieties linked through hydrogen bonds into linear chains. Taking into account the connectivity through cations, two-dimensional layers with a hydrophobic surface are constructed. In tetra(n-propyl)ammonium cyclamate the large, non-coordinating cation apparently prevents the formation of chains and thereby facilitates the centrosymmetric head-to-head discrete dimeric arrangement of the cyclamate moieties.

Solubility of tetracosane in aliphatic alcohols

Abstract Solubilities of tetracosane (C 24 ) in aliphatic alcohols (1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, l-nonanol, 1-decanol, 1-undecanol, 1-dodecanol) have been determined at temperatures ranging from the melting point of the solute to 289 K. Five methods of correlation have been applied: Wilson, simple UNIQUAC, UNIQUAC associated-solution model as well as two modified NRTL equations. The root mean square deviations of the solubility temperatures for all measured data vary from 0.11 K to 2.43 K and depend on the particular equation used. The best solubility correlation has been obtained with the UNIQUAC associated-solution model. In the calculations, the existence of a solid-solid first-order phase transition in tetracosane has also been taken into consideration.

Thermodynamic functions of activation for viscous flow of cholesterol in some non-aqueous solutions

Abstract The viscosities of solutions of cholesterol in benzene, toluene, carbon tetrachloride, chloroform and 1,2-dichloroethane up to 0.4 mol kg −1 at 293, 298, 303, 313, 323 and 333 K have been measured. On the basis of Eyrings theory of rate processes, the molar thermodynamic functions of activation for viscous flow of solution, i.e. the molar Gibbs free energy Δ# Ḡ 1,2 , molar enthalpy, Δ# H H 1,2 and molar entropy, Δ# S 1,2 , and corresponding partial molar quantities of activation for viscous flow of solute and solvent have been determined. Additionally, the viscosity coefficients B and D and their temperature derivatives are calculated and correlated with solvent dielectric parameter β. The influence of the “solvent effect” on the above parameters is discussed on the basis of Eyrings theory of the transition state and the structure of solution.